Melt the butter, add the flour, and when it's bubbling, add the milk, cook into a smooth paste, then stir while cooling.
Season with salt, mix in the 3 egg yolks, then gently fold in the whipped whites of the 3 eggs.
Spread onto a buttered, floured, rimless baking sheet to the thickness of a little finger, and bake in a preheated oven at 180°C for 15-18 minutes, until set.
Meanwhile make the filling: fry the finely chopped mushrooms, onion and parsley in butter, add the ground chicken meat, and add enough broth to make a thick paste.
While the baked béchamel sheet is still warm, spread it with the finished meat filling, then roll it up thinly.
Once cooled, cut into slices, and roll in egg, then breadcrumbs.
Fry in hot lard or oil until golden brown, and serve immediately.
Based on: Malatinszky Fanny szakácskönyve (a classic Hungarian cookbook), modernised. Calories and protein are estimated.